GB2148449A - Shock absorber with fluid end stop - Google Patents

Abstract

The shock absorber comprises a first piston 4 which is slidable in a cylindrical housing 2, a second piston 9 which is slidable between a stop 11 and the end of the housing and fluid communication means 12, 15, 18 to permit a discharge flow of the throttling fluid contained in the cylindrical housing. Over the first part (21) of the stroke, the piston 4 moves at a rate determined by throttle 18 in the cylinder wall (or in the piston). At point 22, the piston 4 contacts the second piston 9 and movement of both pistons over the second part (23) of the stroke is controlled by the rate at which fluid can escape from the chamber 10 through orifice 12 in the second piston 9 (or around its periphery), and thus to the conduit 15. In Fig. 2 (not shown), the cylinder has a larger internal diameter for the second part of the stroke, the second piston has 2 flow paths (48, 60) across it, and the main piston has a pressure relief valve. <IMAGE>

Description

SPECIFICATION Shock absorber of fluid type The present invention concerns fluid-type shock absorbers and more particularly those which have a travel limit stop means. A shock absorber of fluid type is generally of a high complex configuration, but, in diagrammatic terms, such a shock absorber comprises at least a cylinder forming a housing for containing throttle flow fluid and a piston which is slidable in said housing, producing a throttle flow of said fluid, in order to cause damping of a movement.

For certain shock absorbers which may be subjected to very violent shocks, it is necessary for the shock absorber to include, at the position at the end of the travel movement of the piston, a means to produce an even greater and more rapid damping action, such means being known by the generic term travel limit stop means.

Among the known means, there is one such means which comprises for example a plurality of throttle conduits of increasingly reducing sections, with the conduits being closed off as the piston moves towards the end of the housing in the cylinder. By virtue of that arrangement, the device produces a damping action which increases very rapidly, in order to prevent the piston from coming into abutment in particular against the end of the housing. The above-described device undoubtedly has advantages and provides a perfect solution to the problem involved. However, it may sometimes suffer from a disadvantage because it requires a plurality of conduits to permit a flow of the fluid supplying the the housing, and that is not always easy to achieve.It should be noted that the aboveindicated fluid supply conduits permit the throttling fluid to be conducted to cooling means external to the cylinder of the shock absorber. In addition, for shock absorbers which must be subjected to considerable forces, as for example on cross country vehicles, lorries and other armour plated vehicles, it is preferable to minimize the number of apertures, conduits etc. which pass through the walls thereof, in order to make them as rigid as possible and to avoid giving rise thereon to weak points which may cause them to suffer from fracture.

The present invention aims to provide a shock absorber involving a throttling flow of fluid and having a travel limit stop means, which has only a minimum number of throttling conduits, in particular in the structure of the shock absorber, in order to avoid the possibility of its fracturing and which moreover provides for the shock absorber to be simple in design and capable of operating with a very short response time.

According to the present invention there is provided a shock absorber with fluid throttling by means of a piston which is displaceable in a cylinder, comprising a first piston slidable in a cylindrical housing which is closed at at least one end, said first piston being capable of sliding over a first path defining a first portion of said housing and over a second path corresponding to a second portion of said housing, said first piston defining over said second path a space between a portion of its outside surface and the internal portion of said housing; a conduit to permit a flow of throttling fluid, opening into said space;; a second piston which is capable of sliding in said second portion of said housing to form a closed fluid chamber between said second piston and the closed end of said housing and first throttling communication means between the two sides of said second piston, being in this case said chamber and the portion of said space which is disposed between said two pistons; communication means having a pressure drop which is much smaller than said first means permitting communication between the two sides of the two faces of said second piston; and means for forming a continuous closed sealing line around said second communication means when said first piston is in contact with said second piston.

Other features and advantages of the present invention will be apparent from the following description which is given with reference to the accompanying drawings by way of example and without limitation, in which drawings: Figure 1 shows a diagrammatic sectional view of a functional embodiment of a shock absorber according to the invention, and Figures 2A and 2B show cross-sectional views of an embodiment of a shock absorber according to the invention in its industrial configuration, in accordance with the shock absorber as shown in Fig. 1.

Referring more particularly to Fig. 1, shown therein in cross-section and in diagrammatic form is an embodiment of a shock absorber according to the invention.

The shock absorber comprises a hollow cylinder 1 defining a cavity or housing 2 in which a piston 4 is slidable. The piston 4 is fixedly connected to a rod 3. The piston 4 is capable of sliding within the housing 2 against the wall 5 thereof under the effect for example of a force which may be applied to the rod 3. The rod 3 passes into the interior of the housing 2 by way of an opening 6.

Depending on the circumstances, the opening 6 may be sealed or unsealed, if the volume between the piston 4 and the end wall 7 of the cylinder in which the opening 6 is provided is or is not to contain a throttling fluid.

The end 8 of the housing 2 is closed to define a chamber 10 containing a throttling fluid between a second piston 9 and the end 8. The piston 9 is capable of sliding from a starting position as shown in Fig. 1, as defined by mechanical abutments 11 in the housing 2, to move towards the end 8 of the housing 2.

The arrangement also includes, co-operating with the second piston 9, fluid communication means 1 2 which permit a communication to be made between on the one hand the chamber 10 defined between the piston 9 and the end 8 of the housing and on the other hand the portion of the housing which is between the piston 9 and the piston 4, in the housing 2.

The piston 4 is of such a configuration that, between a portion of its outside surface 1 3 which is towards the second piston 9 in the housing 2 and the wall 5 of the housing 2, it delimits a space 14 which is always so defined that, irrespective of the position of the piston 4 in the housing 2, a conduit 15 opens into said space 14, more particularly by way of the opening 16, without the opening ever being closed off by the first piston 4.

In the embodiment of the shock absorber as shown in Fig. 1, the piston 4 is of such a configuration as to have a central portion 1 7 which projects with respect to a portion 1 6 which is in sliding co-operation with respect to the wall 5 of the housing 2, the central portion 1 7 being of a certain predetermined length, and a diameter which is smaller than the diameter of the portion 1 6 so as to define, around the periphery of said central portion 17, at least a part of the above-mentioned space 14.

In this embodiment, the conduit 1 5 that permits the flow of a fluid comprises throttling means which are illustrated by a constriction 18. As stated hereinbefore, the conduit 1 5 permits the fluid to be discharged from or introduced into the housing 2 so that the throttling fluid is subjected to a cooling action, as is well known in relation to this type of shock absorber.

However, it may be envisaged that, for certain uses, this conduit that provides for the flow of fluid may be formed by a calibrated orifice which for example passes directly through the wall 16 of the piston to form a communication between above-defined space 14 and the portion of the housing 2 which is between the piston 4 and the end 7 of the cylinder, through which the rod 3 passes.

Fig. 1 shows in broken lines the limit position of the pistons 4 and 9 when the piston 4 is displced within the housing 2 in such a way that the wall 1 3 of the central portion 1 7 is in a position of bearing against the wall 1 9 of the second piston 9 and has urged the piston 9 towards the end 8 of the housing 2.

Accordingly, the volume of the chamber 10 has been diminished to its minimum, to be almost reduced to a zero value. It will be seen that in the limit position, the space 1 4 is nonetheless still in existence and makes it possible for the conduit 1 5 always to be able to communicate with the space 14, with the end or bottom face 20 of the annular groove defined by the central wall of the piston 4 and the wall 5 of the housing 2 always stopping in a position substantially before the opening 16 of the conduit 15, whereby the conduit 1 5 is never closed off.

It is specified that, for certain design applications of travel limit stop means for such a shock absorber, the conduit 12 which is provided in the second piston 9 constitutes a throttling conduit with a pressure drop which is to be substantially greater than that which is produced in the conduit 15. However, it is also possible to envisage that the conduit 12 which is shown as passing through the piston 9 could be provided in such a way that it is formed by a constriction passage defined between the side wall of the piston 9 and the wall 5 of the housing, that embodiment being more particularly illustrated in Fig. 2.

As mentioned hereinbefore, such a shock absorber makes it possible to provide a travel limit stop action in order to eliminate the danger of rupture in relation to untimely shocks exceeding a certain threshold permitted with the above-mentioned advantages and operates in the following manner: It will first be considered that the shock absorber is in the configuration as shown in solid lines and that, as from that position, the shock absorber is subjected to a substantial shock, the shock being transmitted to the rod 3. In a first phase, the force resulting from that shock begins to be damped by the movement of the piston 4 which displaces the throttling fluid contained in the housing 2 upstream of the piston, so that a flow with a throttling action occurs in the conduit 15, through the constriction 18.This first damping effect is produced by the displacement of the piston 4 over a first path or distance which is diagrammatically indicated at 21, and is concluded at the time at which the wall 1 3 of the central portion 1 7 of the piston 4 comes into abutting contact with the wall 19 of the second piston 9. From that moment, the piston 4 begins to push the second piston 9 to seek to reduce the volume of the chamber 10. The fluid which is contained in the chamber 10 is discharged through the throttl- ing means 1 2 which have a pressure drop that is substantially higher than that of the throttling means 18 contained in the conduit 15. The fluid which pauses through the throttling means 1 2 is discharged through the space 14, by the conduit 15.

As from the above-indicated intermediate position defined by the plane indicated at 22, the piston 4 is displaced over a second path or distance 23, pushing the piston 9 back, and gives rise to an even higher level of damping of the force which is applied to the rod 3, in order to ensure that the piston does not come into violent abutting contact with the end 8 of the housing.

This configuration is particularly advantageous as, for certain embodiments of shock absorbers, in particular for cross country vehicles, it permits the shock absorber to have only a single conduit to provide for the flow of throttling fluid, in particular for feeding fluid to the housing 2, being in this case the conduit 15.

The cylinder 1 can therefore be made with a minimum number of weak points since it has only a single conduit passing through the wall thereof.

The shock absorber which has been described in highly diagrammatic form hereinbefore illustrates the advantage and the aim of the invention, that is to say, to provide a shock absorbing or damping action, or travel limiting stop action, with a single conduit permitting a flow of fluid to the housing 2, it being noted that the conduit could even be provided in the piston 4 for certain uses.

It will be appreciated that such a shock absorber as described hereinbefore could opersate only once under those conditions. It is therefore necessary, when a very substantial shock has been absorbed and the shock has terminated, that the assembly of the components making up the shock absorber return to their original position, and that, in that position, it affords other possibilities of a damping action in relation to successive shocks.

Figs. 2A and 2B illustrate a shock absorber in its industrial form, which makes it possible precisely to achieve a repetitive shock absorbing action.

As Figs. 2A and 2B show the same arrangement but in two different positions, it will be apparent that the same references will denote the same components and that it will be immaterial whether reference is made to one or the other of Figs. 2A and 2B.

As before, the shock absorber comprises a cylinder 30 in which a piston 31 is capable of displacement, being actuated by a rod 32.

Provided in the wall of the piston 31 is a pressure relief valve 33 and a non-return valve 34 which is simply formed by an orifice 35 that passes through the piston, and a flexible closure plate or flap 36 for possibly closing-the opening 37 of the conduit 35 which opens into the part of the cylinder 38 which is defined between the end face 39 of the piston 31 and the end 40 of the cylinder 30. The end 40 of the cylinder 30 comprises an end member 41, the diameter of the internal surface 42 of which is larger than the diameter of the surface 43 of the central portion of the cylinder 30.

Disposed in the above-mentioned portion of the end of the cylinder 30 is a second slidable piston 44 which is of the same diameter as the internal surface 42, which means that the two abutments defining the limit position of the piston 44 which is most remote from the end 40 of the cylinder are defined by the portion of the wall 45 of the cylinder that forms the constriction or step due to the difference in diameter between the surfaces 42 and 43. A spring 46 is also disposed between the wall 47 of the piston 44 that is facing towards the end 40, and said end 40; the spring 46 is operable to hold the piston 44 constantly against the abutments 45 or to urge it towards the abutments 45.Provided at the centre of the piston 44 is an opening 48 which can provide a communication between the chamber 49 defined in the end of the cylinder between the end wall portion 40 and the piston 44 and the chamber 50 in the cylinder, which is between the two pistons 31 and 44. Furthermore, disposed around the opening 48 is a sealing joint 51, the diameter of which is smaller than the diameter of the cylindrical wall surface 43 of the cylinder 30, that is to say in fact, smaller than the diameter of the piston 31.

As shown in Fig. 1, a space has been defined, into which opens a feed conduit.

With reference to the foregoing definition, the space 53 is defined in the embodiment illustrated in Fig. 2A and 2B between the side wall 52 of the piston 31 and the side wall 42 of the end of the cylinder 30. The space 53 can be clearly seen in the configuration of the shock absorber as shown in Fig. 2B, into which opens the conduit 54, the function of which is identical to that of the conduit 1 5 as shown in Fig. 1.

It will be appreciated that the cover member 41 co-operates with the cylinder 30 so as to be sealed thereto, that being effected by a joint 58 as shown in the drawings.

The above-described shock absorber operates in the same manner in regard to its primary functions, as that described with reference to Fig. 1, but it also has other advantages.

For that purpose, it will first be considered that the shock absorber is in the configuration illustrates in Fig. 2A. Those conditions being specified, when the shock absorber is subjected to a substantial force which is for example transmitted to the rod 32, the piston 31 slides inwardly in the cylinder 30, moving towards the end 40 thereof, and displaces the throttling fluid contained in the chamber 50, to produce a flow of fluid in the conduit 54.

That fluid is subjected to a first throttling action which makes it possible to produce a first relatively substantial damping action in respect of the force applied to the rod 32. The piston 31 therefore experiences a first displacement over a first path or distance (as referred to herein before) to move into a halfway position of bearing against the second piston 44. The front face of the piston 31 then bears against the seal 51 and thus, as shown in Fig. 2B, provides for defining an auxiliary chamber 55 which is of constant volume, irrespective of the positions of the two pistons relative to each other, even when they are kept in that position. Accordingly, the volume of oil contained in the auxiliary chamber 55 is equivalent to a closed volume and it cannot therefore flow out of the auxiliary chamber 55.From that intermediate position, and if the force continues to be applied to the rod 32, the piston 31 entrains the piston 44, as the piston 31 moves, and accordingly tends to reduce the volume of the chamber 49. The fluid contained in the chamber 49 is therefore discharged and throttled in the constriction 60 which is defined between the side wall of the piston 44 and the wall 42 of the end cover member of the cylinder 30, giving rise to a much more substantial damping action than that which is produced in the conduit 54. That fluid being throttled between the two side walls, that permits it to flow from the chamber 49 towards the space 53 and then to flow through the conduit 54 in the same manner as described in relation to the arrangement shown in Fig. 1.However, in order to limit the forces produced by means of the above-indicated additional damping action, in order to avoid rupturing the shock absorber, the pressure obtaining within the chamber 49 is limited by the pressure relief valve 33 which is disposed in the piston 31, by virtue of the conduit or opening 48 which permits a communication to be made between the chambers 49 and 55. When the force has been completely damped and the spring 46 has been compressed, the two pistons can thus return to their equilibrium position, the piston 31 under a force which is due for example to the actual weight of the suspension of the vehicle with which the shock absorber is associated, and the piston 41 under the action of the spring 46 which expands, that operation continuing until the side edges of the piston come into contact with the abutments 45.However, as the two pistons have separated, the auxiliary chamber 55 has been opened and can thus be resupplied by means of the fluid which is introduced through the conduit 54, which comes to refill the chamber 50, at a relatively substantial flow rate. Accordingly, the fluid which flows into the chamber 50 can therefore also flow to the chamber 49 through the opening 48 which is of substantial diameter. That flow of fluid then permits the chamber 49 to be resupplied with fluid, to refill it with fluid, thus to permit the piston 44 to return very rapidly to its position of bearing against the abutments 45, to be ready to perform its travel limiting stop function, in the event of a fresh shock. Under these conditions, the two pistons have very quickly returned to their original position and are therefore able again to perform their shock absorbing function, in the event of a further subsequent, highly violent shock.

Thus, a shock absorber having the functions and advantages referred to hereinbefore can be used with particular advantage on heavy vehicles or machines, such as for example cross country vehicles or armour plated vehicles, and therefore provides that such vehicles enjoy a substantial degree of reliability and security in movement thereof and a substantial service life, irrespective of the ground over which they move.

Claims (5)

1. A shock absorber with fluid throttling by means of a piston which is displaceable in a cylinder, comprising a first piston slidable in a cylindrical housing which is closed at at least one end, said first piston being capable of sliding over a first path defining a first portion of said housing and over a second path corresponding to a second portion of said housing, said first piston defining over said second path a space between a portion of its outside surface and the internal portion of said housing; a conduit to permit a flow of throttling fluid, opening into said space;; a second piston which is capable of sliding in said second portion of said housing to form a closed fluid chamber between said second piston and the closed end of said housing and first throttling communication means between the two sides of said second piston, being in this case said chamber and the portion of said space which is disposed between said two pistons; communication means having a pressure drop which is much smaller than said first means permitting communication between the two sides of the two faces of said second piston; and means for forming a continuous closed sealing line around said second communication means when said first piston is in contact with said second piston.

2. A shock absorber as claimed in claim 1, including stop means for defining a limit reference position of said second piston in said cylindrical housing, and means for applying a resilient force between said second piston and said closed end of said housing.

3. A shock absorber as claimed in claim 1 or claim 2, in which said first piston comprises pressure relief valve means.

4. A shock absorber according to any one of the preceding claims, in which said cylindrical housing which is closed at at least one end comprises at least a first and a second portion, said second portion which is disposed at the side of the closed end is larger in section than sslfl first portion, '1W -end piston being slidable in id sac avid portion, and said conduit having its end opening into said second portion.

5. A shock absorber substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.